1. Field of the Invention
The present invention relates to an ionization method for a substance and a mass spectrometry method using the ionization method. The present invention also relates to an extraction method and purification method for a substance.
2. Description of the Related Art
A mass spectrometry method that is one of component analysis methods is a technique which involves ionizing components in a sample and measuring the mass-to-charge ratio (mass number/charge number) thereof.
In recent years, techniques of creating an image of the distribution of components existing on a solid sample surface are developed. For example, the distribution of a particular component is visualized as a mass image, whereby conditions of a sample can be determined. As an example of such techniques, a method of showing data that serves as the basis for a pathological diagnosis, based on a mass image of a pathological specimen including cancer tissue is developed. A mass image is generally acquired by: ionizing a sample at a plurality of measurement points on a sample surface; obtaining the mass-to-charge ratio of the generated ions for each measurement point; and associating a position on the sample surface with ion information. Hence, in order to improve the spatial resolution of the obtained mass image, a technique of ionizing a micro region on the sample surface is required.
For such a technique of ionizing components in a micro region on a sample surface, U.S. Pat. No. 6,566,653 and Dong Weon Lee et al., “Switchable cantilever for a time-of-flight scanning force microscope” Applied Physics Letters, 84, 1558 (2004) each propose a method of ionizing components on a solid substance surface using a cantilever-type probe configured to oscillate. According to this method, the probe has one pointed leading end and another end fixed to a cantilever, and the probe is driven such that the pointed leading end thereof reciprocates between a sample and the front of an ion take-in port of a mass spectrometer. The pointed leading end of the probe comes into contact with a micro region of the sample, so that components of the sample are attached to the pointed leading end of the probe. Then, voltage and laser light are applied to the pointed leading end of the probe in front of the ion take-in port, whereby only the components in the micro region that are attached to the pointed leading end of the probe can be ionized.
Further, Patrick J. Roach et al., “Nanospray desorption electrospray ionization: an ambient method for liquid extraction surface sampling in mass spectrometry” Analyst, 135, pp 2233-2236 (2010) proposes a method of: imparting a solvent to a micro region on a solid sample surface; dissolving components existing in the micro region; and ionizing the dissolved components under an atmosphere pressure. This method uses: a first capillary configured to supply the solvent for dissolving the components in the solid sample, to the sample surface; and a second capillary configured to move a mixture solution in which the components are dissolved in the solvent, to an ionization site. In the state where the two capillaries are close to the solid sample surface, the solvent is supplied thereto by the first capillary, whereby a liquid bridge is formed between the leading ends of the two capillaries and the sample surface. In the liquid bridge, only a contact portion of the solid sample is dissolved, and the dissolved portion is then introduced to the second capillary. A high voltage is applied to the solvent, and ionization is performed at the leading end of the second capillary. This method enables the ionization of the micro region. Further, because the ionization is performed under an atmosphere pressure, the time required for processing can be shortened, and the size of an apparatus can be reduced. Hence, this method is advantageous particularly when a large number of samples are analyzed.
In mass spectrometry for materials of biological origin such as biological tissue, in the case where molecules are non-selectively cut and fragmented during ionization thereof, it becomes difficult to identify components, and hence soft ionization, in which ionization is achieved without breaking biological components, is also required.